The present disclosure relates generally to arc-flash hazard protection systems, and particularly to arc-flash hazard protection systems for medium-voltage three-phase electrical distribution systems.
Three-phase electrical distribution systems are typically classified as high, medium, and low-voltage systems, with nominal operating voltages being on the order of: greater than 50 kilo-Volt (kV) (high-voltage); less than 50 kV and greater than 1 kV (medium-voltage); and, less than 1 kV (low-voltage), for example. Medium-voltage distribution systems in a processing facility, such as but not limited to a paper mill for example, may utilize distribution buses and switchgear that operate at nominal voltages such as 13.8 kV and 4.2 kV, where the switchgear would be rated for 15 kV and 5 kV, respectively. Many such existing facilities have an already established electrical distribution system that includes many miles of copper bus and a plethora of step-down transformers, switchgear, and the like, which can result in costly expenditures where expansions or upgrades are needed. In the 2004 edition of NFPA-70E (National Fire Protection Association, standard 70E), which is the NFPA standard that addresses electrical safety requirements for employee workplaces, a new arc-flash hazard (AFH) protection requirement was established, which prompted existing facilities to assess whether system upgrades were needed.
In view of standards changes, there is a need in the field of existing electrical distribution systems to provide for arc-flash hazard protection while utilizing much of the already existing electrical distribution infrastructure.